Have you looked into the Thomas Borody bacteriotherapy method used in his ME/CFS study, where instead of using FMT, I believe he cultured important anaerobic gut bacteria including Bacteroidetes, Clostridia and Escherichia coli, and placed those in the gut as a sort of super-power probiotic. That might explain his claimed success rate.
See also: https://old.reddit.com/r/HumanMicrobiome/wiki/index#wiki_testing.3A
If these species were available as probiotics, they would be far more effective than the current probiotics available. But because they can occasionally cause an invasive bacterial infection, nobody wants to sell them as probiotics.
I would like to see more studies testing those bacteria, but the fact that he didn't continue with it suggests it wasn't really effective.
I wanted to try to source some of these bacteria for probiotic use (which would have a risk), but could not find any supplier. I believe they are hard to culture anyway, as they are anaerobic and are killed by oxygen.